Slusarchyk et al. in European Application 335,355 disclose that reduction of the diprotected (trans) cyclobutanone of the formula ##STR2## with sodium borohydride or sodium cyanoborohydride gives the racemic (1.alpha.,2.beta.,3.beta.) cyclobutanol of the formula ##STR3## as the minor product which can then be converted to an antiviral agent such as (.+-.)-(1.alpha.,2.beta.,3.alpha.)-2-amino-9-[2,3-bis(hydroxymethyl)cyclob utyl]-1,9-dihydro-6H-purin-6-one.
Bisacchi et al. in U.S. Pat. No. 5,064,961 disclose preparing the optically active form of the purinyl antiviral agent of the formula ##STR4## i.e. [1R-(1.alpha.,2.beta.,3.alpha.)-2-amino-9-[2,3-bis(hydroxymethyl)cyclobuty l]-1,9-dihydro-6H-purin-6-one. Bisacchi et al. disclose preparing this antiviral agent from the intermediate ##STR5## wherein R.sup.4 is a protecting group such as a hindered silyl group, benzyl, substituted benzyl, aroyl, or acyl. Bisacchi et al. prepare this intermediate by treating the cyclobutanone ##STR6## with a reducing agent such as hindered hydride reagents such as lithium tri-sec-butylborohydride, lithium trisiamylborohydride, diisobutylaluminum hydride and the like, preferably lithium trisiamylborohydride, and hindered borane reducing agents such as dicyclohexylborane, disiamylborane, and the like.
Norbeck et al. in European Patent Application 366,059 describe the preparation of this and related purinyl and pyrimidinyl antiviral agents by several routes. One disclosed process utilizes the conversion of the cyclobutanone ##STR7## to the cyclobutanol ##STR8## by treatment with a reducing agent such as sodium
borohydride, sodium cyanoborohydride, or diisobutylaluminum hydride wherein R.sup.28 and R.sup.29 are lower alkyl, aryl, or arylalkyl, i.e., scheme XXIII C.
Ichikawa et al. in European Patent Application 358,154 also disclose the preparation of this and related purinyl and pyrimidinyl antiviral agents. Ichikawa et al. disclose that if the cyclobutanone ##STR9## is reduced with a greatly sterically hindered reactant the 1,2-cis alcohol of the formula ##STR10## is preferentially formed. Examples of sterically hindered reactants are lithium tri(s-butyl)borohydride and di(isobutyl) aluminum hydride and R.sup.4 is a protecting group such as t-butyldiphenylsilyl.
Pariza et al. in European Patent Application 452,729 and Ahmad in European Patent Application 458,643 disclose methods for preparing the optically active cyclobutanone ##STR11##